Gas mixing apparatus



United States Patent 3,081,818 GAS MIXING APPARATUS Frederic F. A.Braeonier, Plainevcaux, and Jean J. L. E.

Riga, Liege, Belgium, assignors to Societe Belge dc LAyote et desProduits Chimiques du Marly, Liege,

Belgium Filed Apr. 3, 1958, Ser. No. 726,248 Claims priority,application Austria Apr. 20, 1957 8 Claims. (Cl. 158-99) This inventionrelates to method and apparatus for mixing fuel and comburent gases forthe combustion of hydrocarbons, and more particularly to burners forpartial combustion of hydrocarbons in the production of less saturatedhydrocarbons.

This invention relates more particularly, but not exclusively, to mixingapparatus of the annular type, in which the gases of a combustiblemixture are led separately and then brought into intimate mixture, whichis then forced into a combustion chamber through a gas distributingdevice.

For feeding burners with gases, it has already been proposed to usedevices of the type comprising an annular pipe surrounding a centralcore. A mixture of hydrocarbon and primary air is led into this annularpipe so that its direction and speed are changed therein. It passesthrough this space with a swirling movement before being brought intocontact with secondary air. Then the mixture of hydrocarbon and primaryair on one hand and the secondary air on the other hand become in theburner separate and swirling layers (US. Patent No.

In the case of a partial combustion of hydrocarbons for conversion intoacetylene and/or olefines and for obtaining the most efficientoperation, the mixture should be homogeneous and should havesubstantially laminar flow before entering the distributor of a burner.

According to this invention, these conditions are obtained with aspecial arrangement which essentially comprises a vertical annularchamber widening downwards, with a gas-distributor screen at its bottomand surround ing a central inverted conical core, the tip of which is atthe center of the distributor, and by a procedure of bringing togetherthe reaction gases in a narrow annular space, passing them along awidening annulus and through said screen to a reaction zone.

To obtain the best conditions regarding the homogeneity of the gaseousreaction mixture, the angle formed with the vertical by the walls ofthis annular device is advantageously between and and preferably near 7.A substantially cylindrical wall portion near the top of said angle andparallel to the axis of the burner delimits on the distributor a centralzone with surface area substantially equal to that of the surroundingannular zone.

FIGURE 1 is a sectional view of one form of themvention.

FIGURE 2 is a sectional view of a modified form of the invent-ion.

The nature of this invention will appear more clearly by the descriptionof a burner schematically represented in vertical section by FIGURE 1,given by way of example.

In such burner, the mixing chamber 1 having a wall 2 of heat-resistantsteel, surrounds a central hollow conical core 3, the wall 4- of whichis also in refractory steel. The end of said core reaches to the center0 of the burner screen 5.

As shown, the mixing chamber 1 consists of an annular space wideningdownwards, until it reaches screen 5 which distributes the gaseousmixture into the combustion chamber 6. The walls 2 and 4 of the mixingchamher are inclined so as to form in the upper part of said chamber anangle of about 7 with the vertical and the projection of said top on thescreen 5 (indicated by dot-dash lines on FIGURE 1) defines an annularsection AB of the screen 5, surrounding a central portion CD, bothportions having substantially equal surfaces.

The central core 3 with its surmounting conical head 7, withtire-resistant steel walls, surrounds an axial pipe 8 for feeding one ofthe two reaction gases. Pipe 9, feeding the other reaction gas,discharges into an annular chamber 10, leading to an annular space 11between head 7 and the upper part of wall 2. The upper edge 12 of thewall 2 is inclined, as shown, so as to insure a uniform pressure dropand a homogeneous distribution of the gas in said space 11. The space 11decreases in cross section in the direction of the flow of the gases.

The space 11 and the interior of mixing chamber 1 are connected by thenarrow annular gap in zone 13. This brings the gaseous reagents intocontact, the wall 4 of the central core being provided with severalperforation rings 14 for injecting into space 11 a fluid from pipe 8.This fluid comes through pipe 8 and the space 7 Within the central core3. Said spaces 11, 13 and 1 thus form an annular convergent-divergentnozzle of the Venturi type.

According to this invention, the device just described may be operatedas follows:

One of the two gases, e.g., the fuel gas, is introduced through pipe 9.It flows upward in the space 11, where, due to the gradual decrease insection, it obtains an increasing yelocity, while its pressuredecreases. The remaining gaseous reagent, e.g., oxygen, fed through pipe8, flows successively through the annular space 3 and openings 14, intothe restricted section of the nozzle in which it is injectedperpendicularly to the direction of the fuel flow while forming aturbulent mixture. This mixture passes then through mixing chamber 1,i.e., the diver-gent portion of the nozzle, by which it is led to thescreen 5 with a substantially laminar movement without any of thegaseous reagents having a preferential dynamic effect.

According to the invention, one can attain a quite uniform oxygencontent throughout the gas at the end of the mixing chamber, a uniformthroughput in each channel of the screen 5 and a better yield ofunsaturated hydrocarbon (e.=g., of acetylene in the case of a partialcombustion burner). Backfires from the combustion chamher 6 to themixing chamber 1 are avoided; and, even if a backfire should occur, itseffects would be substantially reduced by the cooling action of thelower end of the conical core 3.

FIGURE 2 shows another device to be used for the process of thisinvention, in which the gaseous reagents are brought as separateopposite streams into the mixing zone instead of perpendicular flows asin FIGURE 1.

Pipe 9 for feeding the fuel gas enters the annular chamber 10a connectedwith the annular space 11a, as shown; but, instead of the open annularspace continuing at the bottom of space 11a into a Venturi throat, thereis a perforated ring 16, the perforations of which are staggered withrespect to the oxygen distributing perforations 14a.

Both gaseous reagents thus enter as oppositely directed jets at the topof the annular and divergent mixing chamber 1 having a constructionsimilar to that of FIGURE 1. The resulting combustion mixture passeswith substantially laminar flow to the screen 5 which distributes thismixture into the combustion chamber.

Example The burner shown in FIGURE 1 comprises an annular mixing chamber1 of 350 mm. in height and having a mean diameter of 200 mm., with anangle of 14 at the top, between the walls 2 and 4, said chamber beingtopped by an annular zone 13 for contacting the reagents, said zonebeing of 12.5 mm. in radial width at the inlet 13, before theperforations 14, and of 20 mm. in width at the outlet 20. Said annularzone 13 is of 130 mm. in height. The annular distributing space 11 hasan average height of 130 mm. The central core 3 has a total height (fromthe end of 760 mm. and a diameter of 194 mm. at its greatest width. Itsurrounds pipe 8 having a diameter of 140 mm. The wall 4 is providedwith 390 holes having a diameter of 3 mm., and uniformly distributedalong 3 rings spaced 15 mm.

The projection of the mean circumference between the ID. of the shell 2and the OD. of the core 4- delimits on said distributor 5, a surface CDsurrounded with an annular surface AB, both said surfaces havingapproximately the same area. The distributor 5 is of 215 mm. in heightWhile being traversed by 112 pipes having a diameter of 12 mm.

1,125 cubic meters per hour, caluculated to normal temperature andpressure (Nm. /H.) of methane (98% pure and containing 2% of nitrogen)preheated at 600 C. under a pressure of 1.13 atmospheres, absolute(atm., abs.), and fed through pipe 9, are introduced in said mixingdevice, said methane passing through the dis:

tributing space 11 and then through the annular zone 13, at the inlet ofwhich it has a flow rate of 90 m./sec.

610 Nm. /h. of 97% pure oxygen (97% of oxygen and 3% of nitrogen), alsopreheated at 600 C. are also introduced through pipe 8, under a pressureof 1.2 atm. abs. After being passed through the central core 3, saidoxygen is injected into the methane stream through perforations 14, witha linear flow rate of 163 m./sec.

=Both reagents are thereby rapidly contacted in zone 13 and theirmixture is homogenized in chamber 1, before being introduced in thecombustion chamber 6, through distributor 5.

The areas of the surfaces AB and CD being the same, the reagent mixtureis homogeneously distributed in the pipes of distributor 5, thethroughput of the gaseous mixture being substantially the same in eachof said pipes.

The mixture is ignited in said combustion chamber 6 and the methane issubjected to a partial combustion, the flames being stabilized by afurther addition of oxygen (pilot oxygen) of approximately 80 m. /h.

After a partial combustion and quenching of the combustion gases, 2060Nm. /h. of gas (dry gas volume) containing 7.6% of C H are obtained.

This mixing device is constructed with refractory nickel, chrome andmolybdenum steel, preferably the A.I.S.I. steel of the type No. 321 (asidentified by the Steel Products Manual No. 24 of the American Iron andSteel Institute).

As will be evident from the dimensions given above, the tip of the core4 does not extend entirely through the distributor 5, as indicated inFIGS. 1 and 2. Ohviously such extension is unnecessary and the tip needextend only far enough to support the core accurately in the specifiedposition.

We claim:

1. The method of forming a combustible mixture of a hydrocarbon gas andoxygen and of homogenizing the distribution of said mixed gases into areaction chamber which comprises the steps of supplying said gases separately at superatmospheric pressures of approximately the same order ofmagnitude, preheating said separate gases, continually introducing astream of said preheated gaseous hydrocarbon into one end of an annulardistribution chamber of gradually decreasing cross section,homogeneously distributing, and increasing the velocity of, said gasstream in said distribution chamber by passing the said stream through anarrow annular channel,

injecting a plurality of streams of preheated oxygen into theaccelerated stream of hydrocarbon in a midportion of said narrow channelso that these streams of hydrocarbon and oxygen impinge, uniformlymixing said streams in a conical annular duct of expanding cross sectionand passing them through a distributor screen and into a reactionchamber, the flow being maintained in a substantially laminar annularflow and the inner boundary of the annular flow of gases decreasinggradually to a point substantially in center of the distributor whilethe outer boundary increases correspondingly, and uniformly distributingthe mixed gases into the channels of said distributor.

2. An apparatus for mixing reactant gases, such as fuel gas and oxygen,which comprises a mixing chamber having an outer wall which diverges inthe direction of gas fiow from a restricted portion of the chamber atwhich the reactantgases are introduced; a reaction cham ber below themixing chamber; a distributor screen through which the mixed gases passfrom the mixing chamber into the reaction chamber but which serves as abarrier against backfire to confine the reaction to the reactionchamber; a hollow, substantially conical central core enclosing asubstantially frusto-conical cavity therein, said conical core having aconverged end centrally positioned at the distributor screen and a baseportion adjacent the mixing chamber wall at said restricted portion ofsaid mixing chamber at which the reactant gases are introduced, the corewall diverging from the mixing chamber Wall toward said screen, thusforming an annular channel between them, the an le of divergence nearthe most restricted portion of the mixing chamber being between 5 and 10from the vertical, said base portion of said conical core being of suchdiameter that its projection by a perpendicular cylinder dropped fromthe median line of the most restricted portion of the mixing chamber tothe screen defines on said screen a central circular zone and an annularzone, the areas of which are equal; and a pipe extending into saidfrusto-conical cavity, said pipe feeding a reactant gas, the outer wallof said core in the area of the most restricted portion of the mixingchamber having perforations through which this gas may be led into themixing chamber.

3. Apparatus according to claim 2, wherein the gas feeding pipe extendsaxially into said frusto-conical cavity substantially to those portionsof said cavity which are of smallest cross-section.

4. Apparatus according to claim 2 wherein the angle is about 7.

'5. Apparatus according to claim 2, wherein the top of the mixingchamber is provided with perforations for introducing the reactantgases, said perforations being radial with respect to the axis of thechamber.

6. The method of forming a combustible mixture of preheated gases havingcompletely uniform composition which comprises supplying said gasesseparately both at superatmospheric pressures of approximately the sameorder of magnitude, preheating the separate gases, bringing at least oneof said preheated gases to high velocity by passing said gas through avolume of uniformly decreasing cross section culminating in a narrowannulus, separately introducing at least one other of said preheatedgases therein by injecting a plurality of jets of said other gastransversely into the accelerated stream of the first gas in said narrowannulus, and then passing the gases through a duct in an expandingconical annular flow, the flow through said narrow annulus and ductbeing substantially laminar flow in which the inner boundary of theannular gas flow decreased in diameter from said jets through said duct.

7. The method as defined in claim 6 in which the inner boundary of theannular flow of gases decreases gradually to substantially zero.

8. The method as defined in claim 6 in which the inner boundary of theannular flow of gases decreases gradually while the outer boundaryincreases correspondingly.

References Cited in the file of this patent UNITED STATES PATENTS HoffIan. 17, 1911 Dodge June 15, 1926 6 Wolff Jan. 1, 1929 Maxwell July 10,1934 Oldham May 16, 1944 Campbell et a1. Oct. 3, 1950 Lehrer May 6, 1958FOREIGN PATENTS Great Britain Jan. 5, 1955

2. AN APPARATUS FOR MIXING REACTANT GASES, SUCH AS FUEL GAS AND OXYGEN,WHICH COMPRISES A MIXING CHAMBER HAVING AN OUTER WALL WHICH DIVERGES INTHE DIRECTION OF GAS FLOW FROM A RESTRICTED PORTION OF THE CHAMBER ATWHICH THE REACTANT GASES ARE INTRODUCED; A REACTION CHAMBER BELOW THEMIXING CHAMBER; A DISTRIBUTOR SCREEN THROUGH WHICH THE MIXED GASES PASSFROM THE MIXING CHAMBER INTO THE REACTION CHAMBER BUT WHICH SERVES AS ABARRIER AGAINST BACKFIRE TO CONFINE THE REACTION TO THE REACTIONCHAMBER; A HOLLOW, SUBSTANTIALLY CONICAL CENTRAL CORE ENCLOSING ASUBSTANTIALLY FRUSTO-CONICAL CAVITY THEREIN, SAID CONICAL CORE HAVING ACONVERGED END CENTRALLY POSITIONED AT THE DISTRIBUTOR SCREEN AND A BASEPORTION ADJACENT THE MIXING CHAMBER WALL AT SAID RESTRICTED PORTION OFSAID MIXING CHAMBER AT WHICH THE REACTANT GASES ARE INTRODUCED, THE COREWALL DIVERGING FROM THE MIXING CHAMBER WALL TOWARD SAID SCREEN, THUSFORMING AN ANNULAR CHANNEL BETWEEN THEM, THE ANGLE OF DIVERGENCE NEARTHE MOST RESTRICTED PORTION OF THE MIXING CHAMBER BEING BETWEEN 5* AND10* FROM THE VERTICAL, SAID BASE PORTION OF SAID CONICAL CORE BEING OFSUCH DIAMETER THAT ITS PROJECTION BY A PERPENDICULAR CYLINDER DROPPEDFROM THE MEDIAN LINE BY A PERPENDICULAR CYLINDER DROPPED FROM THE MEDIANLINE OF THE MOST RESTRICTED PORTION OF THE MIXING CHAMBER TO THE SCREENDEFINES ON SAID SCREEN A CENTRAL CIRCULAR ZONE